The present invention relates generally to communications devices, and specifically to reduction of power consumption by digital communications transceivers.
The advantage of automatically reducing the power consumption of electronic devices when they are in a link-off state is well known in the art. As devices decrease in size, and the number of devices in the system increases, the importance of power reduction increases, in order to reduce the overall power consumption of the system. This is particularly important in environments where the system is battery-powered.
Local-area networks (LANs) and communication devices transmitting and receiving digital signals commonly operate on standards such as Ethernet 10BASE-T, 100BASE-TX or 100BASE-FX. The 10BASE-T Ethernet standard enables communication at 10 Mb/s using Manchester encoding. The 100BASE-TX standard enables communication at 100 Mb/s using MLT-3 encoding. Manchester encoding and MLT-3 encoding involve transmitting both positive- and negative-going pulses on AC-coupled lines. The 100BASE-FX standard enables communication at 100 Mb/s, using external transceiver devices that transmit to and receive from fiber media.
IEEE specification 802.3, which is incorporated herein by reference, delineates the properties of link pulses. The specification also contains a definition of an autonegotiation mechanism for Ethernet transceivers. When the autonegotiation mechanism is enabled, the mode of operation of an Ethernet transceiver may be automatically switched between 100BASE-TX and 10BASE-T modes, as well as between full- and half-duplex modes.
Adhoc Technologies, Inc., of San Jose, Calif., produces the Trex AH101 device, which is an Ethernet transceiver having a power saving and/or a power down mode. The device may be configured to enter the power saving mode automatically when no signals are sensed on an Ethernet communications line to which it is coupled. The device returns to a normal mode, in which it receives signals, when it detects signal energy on a communications line, or receives a valid signal.
It is an object of some aspects of the present invention to provide a method and apparatus for automatic detection of valid signal data in a communications device.
It is a further object of some aspects of the present invention to provide a method and apparatus for automatic power switching of a communications device.
In some preferred embodiments of the present invention, a signal energy detection system for use in a communications device comprises a digital filter, which analyzes incoming pulses at a plurality of times to make an initial determination of signal energy on a communications line, typically a communication line wherein an Ethernet standard transmission is present. The initial determination is further analyzed in a signal validation machine, which checks a time interval between consecutive signals found in the initial determination, in order to make a more accurate final determination of the presence of valid signal energy on the communications line. The final determination is preferably used to control automatic power switching of the device. The use of the digital filter to make an initial analysis of the incoming pulses, together with the use of the signal validation machine to make a more accurate analysis, enables valid signal pulses to be detected and reduces the chance of a non-valid pulse being assumed to be valid, in a significantly simpler system than is at present known in the art.
The digital filter receives incoming digital pulses, preferably generated by a squelch circuit responsive to the line energy, and checks if respective levels of the pulses at a plurality of preset times, most preferably two times, are above respective predetermined values. If both the levels are above the predetermined values, the filter makes an initial assumption that signal energy is present in the communication line, and sets an output level high.
Preferably, the high output level from the digital filter is transferred to the signal validation machine, which preferably comprises a finite state machine, wherein further analysis of the signal characteristics is made in order to determine if the line energy comprises a valid signal. The signal validation state machine checks the time between consecutive transitions to a high level. If the time between consecutive transitions is within a preset interval, wherein the preset interval is most preferably a function of the clock rate and the temporal separation of sequential idle pulses of the incoming signals, the state machine sets a signal-valid level high indicating that signal energy is present in the communication line. Because a signal-valid level is set high only on receipt of two consecutive transitions within the preset time interval, the output of spurious signal-valid levels is significantly reduced.
The signal-valid level is preferably input to an energy-on signal generator state machine. The energy-on state machine makes a decision when to power-down the device. Its operation depends on an autonegotiation-mode of operation of the device. If the device is in an autonegotiation-enabled mode, then the energy-on state machine monitors the state of an autonegotiation state machine and operates accordingly. If the device is in an autonegotiation-disabled mode, then the energy-on state machine monitors a link state and operates accordingly. A power module of the communications device receives the energy-on signal and, responsive thereto, supplies power to operate modules of the device other than those comprised in the energy detection system. In the event that during a preset time interval the power module determines that the energy-on level is not set high, the power module automatically powers-down the other modules of the transceiver. The modules remain in a powered-down state until the energy-on level is set high again.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a method for determining whether signal data exists on a communication line, including:
receiving a signal from the line;
measuring a level of the received signal at a plurality of predetermined times;
comparing the measured levels with predetermined reference levels so as to identify a plurality of valid data pulses;
measuring a time interval between two or more of the valid data pulses; and
determining that the valid pulses represent signal data responsive to the measured time interval.
Preferably, the method includes switching power to a communication device responsive to the existence of the signal data.
Preferably, switching power to the communication device includes utilizing a state machine to switch the power.
Preferably, receiving the signal data includes selecting a communications standard for use, and comparing the measured levels includes comparing the levels at times determined responsive to selection of the standard.
Alternatively, selecting the standard includes selecting an Ethernet standard.
Alternatively, measuring the time interval between valid pulses includes comparing the time interval with times determined responsive to the standard.
Preferably, comparing the measured levels includes comparing the levels to predetermined positive and negative voltage levels.
Preferably, comparing the measured levels includes comparing the levels at times determined by a transition of a clock signal.
There is further provided, in accordance with a preferred embodiment of the present invention, apparatus for evaluating signals on a communication line, including:
a filter which compares a level of the signals measured at a plurality of predetermined times with predetermined reference levels, and responsive to the comparison, outputs an indication as to whether the signals represent valid data pulses; and
a signal validation machine which receives the indication and responsive thereto compares a time interval between valid pulses with a predetermined reference time interval so as to determine whether the valid pulses comprise signal data.
Preferably, the apparatus includes a power switch which switches power to a communication device responsive to the existence of the signal data.
Alternatively, the power switch includes a state machine.
Preferably, the signal data is transmitted according to a communications standard, and the filter compares the levels at times determined responsive to the standard.
Alternatively, the standard includes an Ethernet standard.
Preferably, the predetermined reference time interval is determined responsive to the standard.
Preferably, the filter includes a plurality of voltage comparators comparing the level of the signals to predetermined positive and negative voltage levels.
Preferably, the filter includes a clock for determining the times of comparison.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: